NameError: name '...' is not defined

I ran into this error while testing a small Python example.

At first I thought it might be a syntax issue, but it turned out I was trying to use a variable that wasn't defined yet.

Error message:

NameError: name 'total' is not defined

What happened

Python tried to use a variable that had not been defined yet.

Example:

x = 10
y = 20

print(total)